1. Field of the Invention
This invention is directed to a process whereby additional oil is obtained from previously spent shale, more specifically the process is directed to a means of treating spent shale with methanol and water to obtain improved yield of shale oil.
2. Description of the Prior Art
Spent shale disposal is a major concern in oil shale development because of the volume of material to be disposed of and the potentially harmful materials it contains. Depending on the oil yield from the shale, aboveground retorting could require as much as 18.5 tons of oil shale mined per cu. meter of oil produced. Although mining and crushing reduces the oil shale pack density and most of the organic material is removed by retorting, the spent shale volume nevertheless becomes substantially greater than the original volume. Thus spent shale as a waste product is expected to become an ever increasing problem as surface shale retorting operations continue to expand. The spent shale may be used for example in back filling of mine areas or other land reclamation operations. Other uses such are, for example, in road construction and as a filler in various reclamation projects.
The specific composition and properties of the spent shale depend on where it was obtained as well as on the retorting method by which it was caused to be spent. Generally speaking, oil shale consists of sedimentary inorganic material that contains complex organic materials of high molecular weight. Thermal decomposition is the primary means used to recover liquid products from the oil shale. Pyrolysis or retorting of the oil shale yields gaseous liquid and solid products. The liquid, which is produced by the pyrolysis, is in the form of vapor or mist as are the noncondensible hydrocarbon gases. The organic carbon which is not recovered as compounds in the gaseous or liquid product is converted to a coke-like deposit and becomes part of the spent shale. The spent shale, that remains after the initial retorting, is of little or no apparent economic value but is the material utilized in this invention.
Eastern U.S. shales for example contain significant amounts of organic carbon. Upon retorting however, only a small proportion of the organic carbon is converted to oil and the rest remains in the spent shale. It is important in the retorting of any oil shale to recover as much of the organic carbon in the form of oil as possible. However, in the case of Eastern shales it seems that the nature of the organic matter limits the amount of oil that may be produced. It has been suggested that the amount of oil that can be produced during retorting is limited because of the relatively large proportion of aromatic carbon in the organic matter. Thus any process that can be devised to improve this conversion and enhance the oil yield is desirable.